Control system of internal combustion engine

ABSTRACT

A control system of an internal combustion engine includes: a pressure detecting mechanism detecting a pressure in a gas passage which is communicated with the engine; and a controller acquiring a reference pressure as the pressure which is detected immediately after the controller is actuated, and controlling an actuator of the engine based on the reference pressure. The controller is inhibited from acquiring the reference pressure as the detected pressure when the controller is re-actuated after the controller is reset due to a factor other than a turned-off operation of an ignition switch.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a control system of an internal combustion engine.

2. Description of the Related Art

A secondary-air supply device is known which supplies secondary air into an exhaust gas passage upstream of an exhaust emission control catalyst (e.g., a three-way catalyst) of the internal combustion engine. The secondary-air supply device includes a secondary-air supply passage that communicates with the exhaust passage, an air pump that pumps air to the secondary-air supply passage, an air switching valve that selectively opens and closes the secondary-air supply passage, and a check valve that is disposed in the secondary-air supply passage downstream of the air switching valve. The secondary-air supply device supplies secondary air into the exhaust passage to increase the concentration of oxygen in exhaust gas supplied to an emission control catalyst during, for example, startup of the engine, and promote oxidation of HC and CO contained in the exhaust gas.

In the secondary-air supply device as described above, if an abnormality occurs to any of components of the secondary-air supply device, such as the air pump, secondary air cannot be appropriately supplied to the exhaust gas flowing in the exhaust passage. Thus, the exhaust emission purification efficiency may be decreased particularly during startup of the engine. Therefore, it has been proposed to provide a pressure sensor on the secondary-air supply passage, and early detect an abnormality of the secondary-air supply device based on a pressure behavior pattern which is detected by the pressure sensor, as disclosed in, for example, Japanese Patent Application Publication No. 2003-83048 (hereinafter, referred to as “JP-A-2003-83048”).

In the system as disclosed in JP-A-2003-83048, an abnormality of the secondary-air supply device is detected based on the pressure behavior pattern detected by the pressure sensor. However, when an absolute-pressure sensor is used as the pressure sensor, it is necessary to detect atmospheric pressure in order to correctly specify the pressure behavior pattern. Because the pressure in the secondary-air supply passage is equal to atmospheric pressure except during secondary air supply, the secondary-air supply device determines the pressure detected by the pressure sensor except during secondary air supply, as atmospheric pressure.

Taking into consideration secondary air is supplied into the secondary-air supply passage during startup of the engine, atmospheric pressure may be detected at a point in time between the time when the ignition switch is turned on and the time when the air pump of the secondary-air supply device is actuated. More specifically, because the electronic control unit (hereinafter, simply referred to as “ECU”) is actuated by turning the ignition switch on, atmospheric pressure may be detected by the pressure sensor after a predetermined period of time (e.g., 15 ms) has been elapsed from the actuation of the ECU.

If, however, the battery voltage drops sharply instantaneously during operation of the engine, the ECU may be reset even during operation of the engine. Therefore, if atmospheric pressure is set to be detected at the point in time as described above, the ECU may be reset and be re-actuated, and atmospheric pressure may be detected even during secondary air supply. In this case, the pressure in the secondary-air supply passage may be erroneously determined as atmospheric pressure even though the pressure in the secondary-air supply passage is higher than atmospheric pressure because secondary air is being supplied, whereby making it difficult to appropriately diagnose a failure in the secondary-air supply device.

SUMMARY OF THE INVENTION

The invention provides a control system of an internal combustion engine that is prevented from acquiring atmospheric pressure erroneously when an ECU is reset during operation of the engine.

A control system of an internal combustion engine according to a first aspect of the invention includes: pressure detecting means for detecting a pressure in a gas passage which is communicated with the internal combustion engine; and control means for acquiring a reference pressure as the pressure which is detected immediately after the control means is actuated, and controlling an actuator of the engine based on the reference pressure. The control means is inhibited from acquiring the reference pressure as the detected pressure when the control means is re-actuated after the control means is reset due to a factor other than a turned-off operation of an ignition switch. During operation of the engine, the control means may be reset due to the factor other than the turned-off operation of the ignition switch. However, if the reference pressure is acquired during the operation of the engine, a pressure different from the actual atmospheric pressure may be detected and determined as the reference pressure. According to the first aspect of the invention, the pressure different from the actual atmospheric pressure is prevented from being detected and determined as the reference pressure.

The control means may be inhibited from acquiring the reference pressure as the detected pressure when the control means is re-actuated after the control means is reset due to a sharp voltage-drop of a power supply during operation of the internal combustion engine.

It may be determined that the control means was reset due to the turned-off operation of the ignition switch when the control means has been kept de-actuated over a predetermined period of time and an internal combustion engine speed has been zero.

The predetermined period of time may be 500 milliseconds.

The control means may acquire the reference pressure after a predetermined delay time elapses from the initiation of the actuation of the control means when it is determined that the control means was reset due to the turned-off operation of the ignition switch.

The predetermined delay time may be 20 milliseconds.

The control system according to the invention may further include: an emission control catalyst that is provided in an exhaust gas passage of the internal combustion engine; and a secondary-air supply device that supplies secondary air into the exhaust gas passage upstream the emission control catalyst. The secondary-air supply device may have air pumping means for pumping the secondary air into a secondary-air passage and switching means for selectively opening and closing the secondary-air passage. The pressure detecting means may be provided upstream of the switching means, and detect a pressure in the secondary-air passage. The control means may determine whether an abnormality of at least one of the air pumping means and the switching means occurs, based on the reference pressure and the pressure detected by the pressure detecting means during operation of the internal combustion engine.

The control system of the invention may further include a throttle valve that is provided in a intake passage of the internal combustion engine. The pressure detecting means may be provided downstream of a throttle valve, and detect a pressure in the intake passage. The control means may control a fuel injection amount to the internal combustion engine, based on the reference pressure, the pressure detected by the pressure detecting means during operation of the internal combustion engine, and an internal combustion engine speed.

The reference pressure may be atmospheric pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further objects, features and advantages of the invention will become apparent from the following description of exemplary embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements, and wherein:

FIG. 1 is a schematic view showing an internal combustion engine in which a control system according to one example embodiment of the invention is installed;

FIG. 2 is a flowchart showing a routine for controlling secondary air supply;

FIG. 3 is a schematic view showing pressure behavior patterns:

FIG. 4 is a flowchart showing a routine for controlling abnormality detection of a secondary-air supply device;

FIG. 5 is a flowchart showing a routine for controlling atmospheric pressure detection:

FIG. 6A to 6H represent a time chart indicating the engine speed, the pressure in a secondary-air supply passage, and the ON/OFF states of an ignition switch, an ECU, a starter motor and an air pump;

FIG. 7 is a flowchart showing a routine for setting of a normal termination history flag; and

FIG. 8 is a flowchart showing a routine for setting of a normal termination flag.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following, a control system of an internal combustion engine according to one example embodiment of the invention will be described with reference to the drawings. FIG. 1 shows the internal combustion engine in which the control system of the invention is installed. The internal combustion engine of FIG. 1 is a direct injection type spark ignition engine. It is, however, to be understood that the control system of the invention is not limitedly installed in this type of engine, but may also be installed in other types of spark ignition engines or compression self-ignition type engines.

Referring to FIG. 1, an engine body 1, a cylinder block 2, a piston 3 that reciprocates in the cylinder block 2, a cylinder head 4 that is fixed onto the cylinder block 2, a combustion chamber 5 that is formed between the piston 3 and the cylinder head 4, an intake valve 6, an intake port 7, an exhaust valve 8 and an exhaust port 9 are illustrated. As shown in FIG. 1, an ignition plug 10 is disposed in a middle portion of the inner wall of the cylinder head 4, and a fuel injection valve 11 is disposed in a peripheral portion of the inner wall of the cylinder head 4. A cavity 12 that extends from below the fuel injection valve 11 to below the ignition plug 10 is formed in the top face of the piston 3.

The intake port 7 of each cylinder is connected to a surge tank 14 via a corresponding intake manifold 13, and the surge tank 14 is connected to the air cleaner 16 via an intake duct 15. A throttle valve 18 driven by a stepping motor 17 is disposed in the intake duct 15. On the other hand, the exhaust port 9 of each cylinder is connected to the exhaust manifold 19, and the exhaust manifold 19 is connected to a catalytic converter 22 incorporating an exhaust emission control catalyst (e.g., a three-way catalyst) 21, via an exhaust pipe 20.

The internal combustion engine of this embodiment includes a secondary-air supply device 25. The secondary-air supply device 25 has a secondary-air supply passage 26 that communicates with the exhaust manifold 19. The secondary-air supply passage 26 also communicates with the intake duct 15 downstream of the air cleaner 16 and upstream of an air flow meter 49 which will be described later. An air pump 27 which is driven by an electric motor, an air switching valve (ASV) 28 and a check valve 29 are disposed in the secondary-air supply passage 26, from the intake duct 15 toward the exhaust manifold 19. A pressure sensor 30 that detects the pressure in the secondary-air supply passage 26 is provided between the air pump 27 and the ASV 28.

An ECU 40 consists of a digital computer, and includes ROM (i.e., read-only memory) 42, RAM (i.e., random access memory) 43, CPU (i.e., microprocessor) 44, an input port 45 and an output port 46, which all are connected to each other via a two-way bus 21. The air flow meter 49 that detects the flow rate of air flowing in the intake duct 15 is mounted in the intake duct 15 upstream of the throttle valve 18, and an air-fuel ratio sensor 50 is mounted in the exhaust manifold 19. Output signals from the air flow meter 49, air-fuel ratio sensor 50 and the pressure sensor 30 are transmitted to the input port 45 via corresponding A/D (i.e., analog/digital) converters 47.

A load sensor 52 is connected to an accelerator pedal 51. The load sensor 52 generates an output voltage, which is proportional to the depression amount of the accelerator pedal 51. The output voltage from the load sensor 52 is also transmitted to the input port 45 via a corresponding A/D converter 47. A crank angle sensor 53 generates output pulses each time the crankshaft rotates, for example, by 30 degrees. The output pulses are transmitted to the input port 45. The CPU 44 calculates the engine speed based on the output pulses of the crank angle sensor 53. On the other hand, the output port 46 is connected to the ignition plug 10, the fuel injection valve 11, the stepping motor 17, the air pump 27 and the ASV 28, via corresponding drive circuits 48.

Next, the secondary-air supply device 25 according to the embodiment will be explained. The secondary-air supply device 25 may be effectively used under circumstances where the air-fuel ratio of exhaust gas is rich and the temperature of the exhaust emission control catalyst 21 has not been sufficiently raised, as is often observed during cold starting of the engine. Namely, The secondary-air supply device 25 may be effectively used under circumstances where HC and CO which are contained in the exhaust gas cannot be sufficiently converted into harmless substances.

More specifically, under the circumstances as described above, the ASV 28 is opened and the air pump 27 is driven. As a result, a part of air that has passed through the air cleaner 16 is supplied into the exhaust manifold 19 via the secondary-air supply passage 26. With air thus supplied, the concentration of oxygen in the exhaust gas flowing in the exhaust manifold 19 is increased, and the air-fuel ratio of the exhaust gas becomes lean from a richstate. Thus, HC and CO which are contained in the exhaust gas are burned in the exhaust emission control catalyst 21 while the exhaust gas is passing the exhaust emission control catalyst 21, so that purification of the exhaust gas is promoted, and the temperature of the exhaust gas is increased, resulting in an increase in the temperature of the exhaust emission control catalyst 21. That is, the secondary-air supply device 25 supplies secondary air to the exhaust gas during, for example, cold starting of the engine to suppress the emission of the harmful exhaust gas.

FIG. 2 is a flowchart of a routine for controlling secondary air supply with the secondary-air supply device 25. In the routine shown in FIG. 2, it is initially determined in step S10 whether conditions for executing secondary air supply are satisfied. The ECU 40 determines whether the conditions for executing secondary-air supply are satisfied, based on the engine coolant temperature, intake air temperature, engine load and so forth. If it is determined in step S10 that the conditions for executing secondary-air supply are not satisfied (for example, when the engine is not operating under cold starting), secondary-air is not supplied into the exhaust manifold 19, and this routine for controlling secondary air supply is finished.

On the other hand, if it is determined in step S10 that the conditions for executing secondary-air supply are satisfied, the ECU 40 proceeds to step S11. In step S11, it is determined whether an abnormality of the secondary-air supply device 25 has been detected (this abnormality detection control of the secondary-air supply device 25 will be described later). If it is determined in step S11 that an abnormality of the secondary-air supply device 25 has been already detected, this routine for controlling secondary air supply is also finished. In this manner, the secondary air is prevented from being supplied when an abnormality occurs in the secondary-air supply device 25.

On the other hand, if it is determined in step S11 that any abnormalities of the secondary-air supply device 25 have not been detected, the ECU 40 proceeds to step S12. In step S12, the air pump 27 is actuated, and the ASV 28 is opened, so that secondary air is supplied into the exhaust manifold 19.

In the following step S13, it is determined whether conditions for finishing secondary-air supply are satisfied. The ECU 40 determines whether the conditions for finishing secondary-air supply are satisfied, based on, for example, an elapsed time from the start of secondary air supply, and the temperature of the exhaust emission control catalyst 21. If it is determined in step S13 that the conditions for finishing secondary-air supply are not satisfied, step S13 is repeatedly executed. Thus, the secondary air supply is continued until the conditions for finishing secondary-air supply are satisfied.

If it is determined in step S13 that the conditions for finishing secondary-air supply are satisfied, the ECU 40 proceeds to step S14. In step S14, the operation of the air pump 27 is stopped and the ASV 28 is closed, so that the secondary air supply into the exhaust manifold 19 is stopped.

In the meantime, if an abnormality occurs in any components of the secondary-air supply device 25, such as the air pump 27, ASV 28 and the check valve 29, secondary air cannot be appropriately supplied to the exhaust gas during, for example, cold starting of the engine, resulting in the emission of the harmful exhaust gas. Therefore, the secondary-air supply device 25 according to the embodiment has the function that detects an abnormality in the components of the secondary-air supply device 25. More specifically, an abnormality in the components of the secondary-air supply device 25 is detected based on the pressure behaviors (or variations in the pressure) of air in the secondary-air supply passage 26. The pressure of air is detected by the pressure sensor 30. In the following, there will be described an example of detection of abnormalities in the components of the secondary-air supply device 25, based on the pressure behaviors of air in the secondary-air supply passage 26.

FIG. 3 is a schematic view showing the pressure behaviors of air in the secondary-air supply passage 26 between the air pump 27 and the ASV 28, that is, patterns of pressure behaviors detected by the pressure sensor 30. TABLE 1 shows the relationships between the combinations of the operating states of the air pump 27 and the ASV 28, and pressure behavior patterns. The operating states of the air pump 27 and the ASV 28 may be estimated based on the detected pressure behavior patterns from these relationships.

TABLE 1 Air Pump ASV Pressure Behavior Pattern Operating Open 1 Stopped Open 2 Operating Closed 3 Stopped Closed 4

When the air pump 27 is actuated and the ASV 28 is opened, secondary air supply is performed, so that the pressure behavior pattern becomes “PATTERN 1” as shown in FIG. 3. On the other hand, when the air pump 27 is stopped and the ASV 28 is closed, the secondary air supply is stopped, so that the pressure behavior pattern becomes “PATTERN 4” as shown in FIG. 3. Accordingly, if any abnormalities do not exist in the secondary-air supply device 25, the pressure behavior pattern becomes “PATTERN 1” while the secondary air is being supplied, and the pressure behavior pattern becomes “PATTERN 4” while the secondary air is not being supplied. Thus, if patterns of pressure behaviors detected by the pressure sensor 30 differ from “PATTERN 1” or “PATTERN 4” in FIG. 3, it is assumed that an abnormality exists in the air pump 27 or the ASV 28.

More specifically, TABLE 2 below shows the relationships between the pressure behavior patterns and abnormalities in the air pump 27 and the ASV 28. The pressure behavior patterns in TABLE 2 are divided into a pattern while the secondary air is being supplied and a pattern while the secondary air is not being supplied, respectively. In TABLE 2, “O” indicates that the air pump 27 or ASV 28 operates normally, and “X” indicates that an abnormality exists in the air pump 27 or ASV 28. As shown in Mode 2 of TABLE 2, when no abnormality exists in the air pump 27 whereas an abnormality exists in the ASV 28 such that the ASV 28 is kept open all the time, the air pump 27 is actuated and the ASV 28 is opened while the secondary air is being supplied. Thus, the pressure behavior pattern in this case becomes “PATTERN 1”. Meanwhile, because the air pump 27 is stopped and the ASV 28 is still opened while the secondary air is not being supplied, the pressure behavior pattern becomes “PATTERN 2”. Accordingly, if the pressure behavior pattern becomes “PATTERN 1” while the secondary air is being supplied, and becomes “PATTERN 2” while the secondary air is not being supplied, it may be estimated that an abnormality has occurred in the ASV 28, and the ASV 28 is kept open all the time.

TABLE 2 Pressure Behavior Pattern During During Mode Air Pump ASV supply stopping 1 ◯ ◯ 1 4 2 ◯ X (kept open) 1 2 3 ◯ X (kept closed) 3 4 4 X (kept operating) ◯ 1 3 5 X (kept operating) X (kept open) 1 1 6 X (kept operating) X (kept closed) 3 3 7 X (kept inoperative) ◯ 2 4 8 X (kept inoperative) X (kept open) 2 2 9 X (kept inoperative) X (kept closed) 4 4

Similarly, an abnormality of the air pump 27 may be detected when the air pump 27 is kept operating even while the secondary air is not being supplied as well as while the secondary air is being supplied (“kept operating” in TABLE 2), or when the air pump 27 is kept inoperative even while the secondary air is being supplied as well as while the secondary air is not being supplied (“kept inoperative” in TABLE 2). Also, an abnormality of the ASV 28 may be detected when the ASV 28 is kept closed all the time as well as when the ASV 28 is kept open all the time (“kept closed” in TABLE 2).

Thus, the secondary-air supply device 25 of the embodiment checks the pressure behavior pattern while the secondary air is being supplied and while the secondary air is not being supplied, respectively, so that may detect abnormalities in the air pump 27 and the ASV 28.

FIG. 4 is a flowchart of a routine for controlling abnormality detection of the secondary-air supply device 25. In the routine shown in FIG. 4, it is initially determined in step S20 whether preconditions for detecting an abnormality in the secondary-air supply device are satisfied. The preconditions for detecting the abnormality may be satisfied when all of the following conditions are satisfied which include: (1) the battery voltage is sufficiently high enough to implement the abnormality detecting process, (2) the engine has been started, and (3) atmospheric pressure has been acquired through atmospheric-pressure detection control which will be described later. If it is determined in step S20 that the preconditions for detecting the abnormality have not been satisfied, this routine is finished. On the other hand, if it is determined that the preconditions for detecting the abnormality have been satisfied, the ECU 40 proceeds to step S21.

In step S21, it is determined whether a condition for detecting the pressure in the secondary-air supply passage 26 when the secondary air is being supplied is satisfied. This condition is satisfied when, for example, the air pump 27 is operating under a stable state after a predetermined time has elapsed from the start of the secondary air supply, and it is presumed from the engine speed, engine load, etc., that the engine is operating under an idling state. That is, this condition is satisfied when the pressure in the secondary-air supply passage 26 may be easily detected when the secondary air is being supplied. If it is determined in step S21 that the condition for detecting the pressure in the secondary-air supply passage 26 when the secondary air is being supplied is not satisfied, step S21 is repeatedly executed until this condition is satisfied. Subsequently, if it is determined in step S21 that this condition is satisfied, the ECU 40 proceeds to step S22 to cause the pressure sensor 30 to detect the pressure in the secondary-air supply passage 26.

Next, it is determined in step S23 whether a condition for detecting the pressure in the secondary-air supply passage 26 when the secondary air is not being supplied is satisfied. This condition is satisfied when, for example, the pressure in the secondary-air supply passage 26 is under a stable state after a predetermined time has elapsed from the stop of the secondary air supply. That is, this condition is satisfied when the pressure may be easily detected when the secondary air is not being supplied. If it is determined in step S23 that the condition for detecting the pressure in the secondary-air supply passage 26 when the secondary air is not being supplied is not satisfied, step S23 is repeatedly executed until this condition is satisfied. Subsequently, if it is determined in step S23 that this condition is satisfied, the ECU 40 proceeds to step S24 to cause the pressure sensor 30 to detect the pressure in the secondary-air supply passage 26.

Next, it is determined in step S25 whether an abnormality exists at least in the air pump 27 and the ASV 28, based on the pressures detected in step S22 and step S24 and the pressure behavior patterns shown in TABLE 2. After execution of step S25, this routine is finished.

In the meantime, the pressure value “0” as shown in FIG. 3 represents atmospheric pressure. It is, therefore, necessary to detect atmospheric pressure in advance in order to determine the pressure behavior patterns such as PATTERN 1 through PATTERN 4. On the other hand, if atmospheric pressure is not detected in advance, it becomes difficult to correctly determine to which pattern the pressure behavior corresponds. Therefore, an abnormality of the secondary-air supply device 25 may be erroneously determined. Here, the atmospheric pressure may be regarded as “reference pressure” of the present invention.

In the secondary-air supply device 25 of the embodiment, therefore, the pressure sensor 30 detects the pressure of air in the secondary-air supply passage 26 before the engine is started and before the air pump 27 is actuated, for example, after the predetermined time (e.g., 20ms; hereinafter referred to as “detection delay time”) has elapsed from the actuation of the ECU 40. At this timing, the pressure of air in the secondary-air supply passage 26 is normally equal to atmospheric pressure, and therefore, the atmospheric pressure may be relatively accurately detected.

FIG. 5 is a flowchart of a routine for controlling atmospheric pressure detection. In the routine shown in FIG. 5, it is initially determined in step S27 whether conditions for acquiring atmospheric pressure are satisfied. The atmospheric-pressure acquisition conditions are satisfied when the detection delay time has elapsed from the actuation of the ECU 40, prior to startup of the engine, and a normal termination flag Xne is also set to 1. The normal termination flag Xne will be described later.

If it is determined in step S27 that the atmospheric-pressure acquisition conditions are satisfied, the ECU 40 proceeds to step S28 to cause the pressure sensor 30 to detect the pressure in the secondary-air supply passage 26 so that this detected pressure is regarded as the atmospheric pressure. On the other hand, if it is determined in step S27 that the atmospheric-pressure acquisition conditions are not satisfied, step S28 is skipped, and the atmospheric pressure is not acquired. Therefore, if the atmospheric pressure is not acquired, it is determined in step S20 of FIG. 4 that the preconditions for detecting an abnormality in the secondary-air supply device 25 are not satisfied. As a result, the abnormality detection for the secondary-air supply device 25 is not carried out.

In some rare cases, the pressure in the secondary-air supply passage 26 may not be equal to the atmospheric pressure even though the detection delay time has elapsed from the actuation of the ECU 40. An example of such cases will be described with reference to FIG. 6A to 6H, also called “FIG. 6”.

FIG. 6 is a time chart indicating the engine speed (NE), the pressure in the secondary-air supply passage 26, and the ON/OFF states of the ignition switch (IG), the ECU 40, the starter motor and the air pump 27. When the ignition switch is turned on at time t₁, the ECU 40 is actuated at the same time. At time ti, because the starter motor has not been actuated yet, the engine speed is zero, and the air pump 27 has not been actuated. Therefore, the pressure of air in the secondary-air supply passage 26 is equal to atmospheric pressure. After the detection delay time Δt has elapsed from the actuation of the ECU 40, the pressure sensor 30 detects the pressure of air in the secondary-air supply passage 26 (at time t₂). Because the pressure of air in the secondary-air supply passage 26 is still equal to atmospheric pressure at time t₂, it is possible to accurately determine the atmospheric pressure by causing the pressure sensor 30 to detect the pressure in the secondary-air supply passage 26 (as indicated by a circle at time t₂ in FIG. 6).

Subsequently, the starter motor is driven (at time t₃) to increase the engine speed, and the engine is thus started. When the engine speed becomes equal to or higher than a specified speed (for example, 400 rpm), the air pump 27 is actuated (at time t₄), and the pressure of air in the secondary-air supply passage 26 increases. Thus, the atmospheric pressure may be accurately detected by the pressure sensor 30 at time t₂ as long as the engine is started normally.

If, however, the battery voltage drops sharply instantaneously during operation of the engine due to, for example, turning on operation of a starter switch by the driver, the ECU 40 may be reset. If the ECU 40 is reset as in this case, operations of various actuators returns to the initial states, and therefore, the air pump 27 stops operating while the ASV 28 is closed (at time t₅). However, the air pump 27 keeps rotating for a while under the inertia even if the air pump 27 stops operating, and the ASV 28 is closed. As a result, the air in the secondary-air supply passage 26 is less likely to be released out of the secondary-air supply passage 26. That is, the pressure of air in the secondary-air supply passage 26 is not immediately decreased but gradually decreased. Here, the battery may be regarded as “power supply” of the invention.

On the other hand, the ECU 40 is actuated immediately (at time t₆) after being reset. The pressure sensor 30 detects the pressure of air in the secondary-air supply passage 26 at time t₇ after the detection delay time At has elapsed from the re-actuation of the ECU 40. At time t₇, however, the residual pressure exists in the secondary-air supply passage 26 as shown in FIG. 6, and therefore the pressure of air in the secondary-air supply passage 26 is higher than the atmospheric pressure (as indicated by a circle at time t₇ in FIG. 6). Accordingly, if the pressure of air in the secondary-air supply passage 26 is detected by the pressure sensor 30 at time t₇, and this pressure is determined to the atmospheric pressure, abnormalities in the secondary-air supply device 25 cannot be accurately detected.

In the secondary-air supply device of the embodiment, therefore, if the ECU 40 is re-actuated because the ECU 40 has been reset due to a factor other than turned off of the ignition switch, the pressure sensor 30 is inhibited from detecting the pressure of air in the second-air supply passage 26 and acquiring this pressure as atmospheric pressure. More specifically, the normal termination flag Xne is used, which is set to 1 when the ECU 40 has been normally reset due to turn-off of the ignition switch, and is set to zero when the ECU 40 has been reset due to the operation other than turn-off of the ignition switch. Thus, the atmospheric pressure is actually acquired if the normal termination flag Xne is set to 1, and the atmospheric pressure is not acquired if the normal termination flag Xne is set to zero.

Here, the normal termination flag Xne may be changed based on a normal termination history flag Xner, which will be described later. More specifically, the normal termination flag Xne is set to 1 when the normal termination history flag Xner is set to 1 upon the actuation of the ECU 40. On the other hand, the normal termination flag Xne is set to zero when the normal termination history flag Xner is set to zero upon the actuation of the ECU 40.

The normal termination history flag Xner is set to 1 when the ECU 40 is normally reset due to turn-off of the ignition switch. More specifically, the normal termination history flag Xner is set to 1 when the ignition switch is being held under the turned off state over a predetermined period of time (for example, 500 ms) or longer after the ignition switch has been turned off, and when the engine has stopped operating (for example, when the engine speed has been equal to zero). Because the ECU 40 may receive a signal of “ignition-off” (i.e., turned off of the ignition switch) due to noise or the like, the ignition switch is necessary to be held under the turned off state over the predetermined period of time. As a result, the ECU 40 may be not affected by the noise or the like. The normal termination history flag Xner is set to zero when the ECU 40 has acquired atmospheric pressure. More specifically, the normal termination history flag Xner is set to zero when the atmospheric pressure has been appropriately detected by the pressure sensor 30 after the detection delay time had been elapsed from turning the ignition switch on, and when the engine has been started (for example, when the engine speed has been equal to or higher than 400 rpm).

In the manner as described above, if the pressure of air in the secondary-air supply passage 26 is not equal to atmospheric pressure even after the detection delay time has been elapsed from the actuation of the ECU 40, the pressure which has been detected by the pressure sensor 30 is not acquired as the atmospheric pressure. Therefore, abnormalities in the secondary-air supply device 26 is prevented from being erroneously detected.

FIG. 7 is a flowchart of a routine for setting the normal termination history flag Xner. This routine shown in FIG. 7 is executed as an interrupt routine at fixed time intervals. Referring to FIG. 7, it is initially determined in step S30 whether conditions for setting the normal termination history flag Xner are satisfied. These conditions are satisfied when, for example, the ignition switch is being held under the turned off state over a predetermined period of time (e.g., 500 ms) from turning the ignition switch off, and the engine has stopped operating, as described above. If it is determined in step S30 that the conditions for setting the normal termination history flag Xner are satisfied, the ECU 40 proceeds to step S31 to set the normal termination history flag Xner to 1. On the other hand, if it is determined in step S30 that the conditions for setting the normal termination history flag Xner are not satisfied, the ECU 40 skips the step S31.

In the following step S32, it is determined whether conditions for clearing the normal termination history flag Xner are satisfied. These conditions are satisfied when the atmospheric pressure has been appropriately detected by the pressure sensor 30 after the detection delay time had been elapsed from turning the ignition switch on, and the engine has been started, and when the normal termination history flag Xner is being set to 1. If it is determined in step S32 that the conditions for clearing the normal termination history flag Xner are satisfied, the ECU 40 proceeds to step S33 to clear the normal termination history flag Xner to zero. On the other hand, if the conditions for clearing the normal termination history flag Xner are not satisfied, the ECU 40 skips the step S33.

FIG. 8 is a flowchart of a routine for setting the normal termination flag Xne. This routine shown in FIG. 8 is executed as an interrupt routine at fixed time intervals. Referring to FIG. 8, it is initially determined in step S40 whether the ECU 40 is actuated at this time (i.e., at the time when step S40 is executed). If it is determined in step S40 that the ECU 40 is actuated, the ECU 40 proceeds to step S41. In step S41, the value of the normal termination flag Xne is made equal to the value of the normal termination history flag Xner. On the other hand, if it is determined in step S40 that the ECU 40 is not actuated, the ECU 40 skips the step S41.

In the embodiment as described above, the control system of the invention is applied to the secondary-air supply device, and inhibits from detecting atmospheric pressure despite the actuation of the ECU except when the engine has normally stopped operating. It is, however, to be understood that the control system of the invention may be applied to other devices. In particular, the control system may be applied to a mechanism for detecting atmospheric pressure with a pressure sensor that detects a pressure in a region where the pressure becomes equal to atmospheric pressure before startup of the engine and becomes different from the atmospheric pressure during operation of the engine. An example of the above-mentioned device is so called “D-Jetronic” which is a registered trademark of Bosch Corporation (hereinafter simply referred to as “D-J device”). The D-J device controls the fuel injection amount based on the pressure in an intake passage that has been detected by an intake-passage pressure sensor for detecting the pressure in the intake passage, rather than the flow rate of intake air that has been detected by the air flow meter.

More specifically, in the D-J device, the target fuel injection amount and target ignition timing are calculated based on the engine speed and the pressure in the intake passage which is detected by the intake-passage pressure sensor for detecting the pressure in the intake passage (including an intake duct, a surge tank and an intake manifold) downstream of the throttle valve. However, if the vehicle runs at the high altitude, the fuel injection amount for providing the same air-fuel ratio as compared to the air-fuel ratio on level ground increases even though the pressure in the intake passage is the same as compared with the case where the vehicle runs on level ground at standard atmospheric pressure because atmospheric pressure decreases as the altitude increases. With regard to the ignition timing, the output torque is reduced when the vehicle runs at a high altitude if the same ignition timing as that of the vehicle running on level ground is employed with respect to the same load. Therefore, it is necessary to correct the target fuel injection amount and target ignition timing depending upon the atmospheric pressure, which makes it necessary to acquire the atmospheric pressure in advance.

In the D-J device, therefore, the pressure is detected by the intake-passage pressure sensor after the detection delay time has been elapsed from the actuation of the ECU 40, and this pressure is acquired as atmospheric pressure, as with the secondary-air supply device. In the D-J device, the pressure in the intake passage which is detected after the ECU 40 is re-actuated may be erroneously acquired as atmospheric pressure if the ECU 40 is reset due to a factor other than turned-off of the ignition switch. Consequently, the fuel injection amount and the ignition timing cannot be appropriately controlled.

However, according to the D-J device employing the control system of the invention, the atmospheric pressure is inhibited from being acquiring when the ECU 40 has been reset due to a factor other than turned-off of the ignition switch and has been re-actuated. Thus, the D-J device is prevented from being inappropriately controlled due to inaccuracy in the acquired atmospheric pressure.

While the invention has been described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the described embodiments or constructions. To the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the exemplary embodiments are shown in various combinations and configurations, other combinations and configurations, including more, less or only a single element, are also within the scope of the invention. 

1. A control system of an internal combustion engine, comprising: a throttle valve that is provided in an intake passage of the internal combustion engine; an emission control catalyst that is provided in an exhaust gas passage of the internal combustion engine; a secondary supply device including: a secondary air supply passage that communicates with the intake passage downstream the throttle valve and the exhaust gas passage upstream the emission control catalyst: air pumping means for pumping the secondary air into the secondary air passage; switching means for selectively opening and closing the secondary air passage; pressure detecting means for detecting a pressure in the secondary air passage and that is provided upstream of the switching means; and control means for acquiring a reference pressure as the pressure which is detected immediately after the control means is actuated, and controlling an actuator of the internal combustion engine based on the reference pressure, wherein the control means is inhibited from acquiring the detected pressure when the control means is re-actuated after the control means is reset due to a factor other than turned-off operation of an ignition switch.
 2. The control system of the internal combustion engine according to claim 1, wherein the control means is inhibited from acquiring the reference pressure as the detected pressure when the control means is re-actuated after the control means is reset due to a sharp voltage-drop of a power supply during operation of the internal combustion engine.
 3. The control system of the internal combustion engine according to claim 1, wherein it is determined that the control means was reset due to the turned-off operation of the ignition switch when the control means has been kept de-actuated over a predetermined period of time and an internal combustion engine speed has been zero.
 4. The control system of the internal combustion engine according to claim 3, wherein the predetermined period of time is 500 milliseconds.
 5. The control system of the internal combustion engine according to claim 3, wherein the control means acquires the reference pressure after a predetermined delay time elapses from the initiation of the actuation of the control means when it is determined that the control means was reset due to the turned-off operation of the ignition switch.
 6. The control system of the internal combustion engine according to claim 5, wherein the predetermined delay time is 20 milliseconds.
 7. The control system of the internal combustion engine according to claim 1, wherein: the control means determines whether an abnormality of at least one of the air pumping means and he switching means occurs, based on the reference pressure and the pressure detected by the pressure detecting means during operation of the internal combustion engine.
 8. The control system of the internal combustion engine according to claim 1, wherein: the control means controls a fuel injection amount to the internal combustion engine, based on the reference pressure, the pressure detected by the pressure detecting means during operation of the internal combustion engine, and an internal combustion engine speed.
 9. The control system of the internal combustion engine according to claim 1, wherein the reference pressure is atmospheric pressure. 